Enceladus’ Salty Surprise

byJason MajoronJune 22, 2011

Enceladus' signature ice geysers in action. NASA / JPL / SSI

Researchers on the Cassini mission team have identified large salt grains in the plumes emanating from Saturn’s icy satellite Enceladus, making an even stronger case for the existence of a salty liquid ocean beneath the moon’s frozen surface.

Cassini first discovered the jets of water ice particles in 2005; since then scientists have been trying to learn more about how they behave, what they are made of and – most importantly – where they are coming from. The running theory is that Enceladus has a liquid subsurface ocean of as-of-yet undetermined depth and volume, and pressure from the rock and ice layers above combined with heat from within force the water up through surface cracks near the moon’s south pole. When this water reaches the surface it instantly freezes, sending plumes of ice particles hundreds of miles into space.

Enceladus inside the E ring

Much of the ice ends up in orbit around Saturn, creating the hazy E ring in which Enceladus resides.

Although the discovery of the plumes initially came as a surprise, it’s the growing possibility of liquid water that’s really intriguing – especially that far out in the Solar System and on a little 504-km-wide moon barely the width of Arizona. What’s keeping Enceladus’ water from freezing as hard as rock? It could be tidal forces from Saturn, it could be internal heat from its core, a combination of both – or something else entirely… astronomers are still hard at work on this mystery.

Now, using data obtained from flybys in 2008 and 2009 during which Cassini flew directly through the plumes, researchers have found that the particles in the jets closest to the moon contain large sodium- and potassium-rich salt grains. This is the best evidence yet of the existence of liquid salt water inside Enceladus – a salty underground ocean.

“There currently is no plausible way to produce a steady outflow of salt-rich grains from solid ice across all the tiger stripes other than salt water under Enceladus’s icy surface.”

– Frank Postberg, Cassini team scientist, University of Heidelberg, Germany

Looking down into a jetting "tiger stripe"

If there indeed is a reservoir of liquid water, it must be pretty extensive since the numerous plumes are constantly spraying water vapor at a rate of 200 kg (400 pounds) every second – and at several times the speed of sound! The plumes are ejected from points within long, deep fissures that slash across Enceladus’ south pole, dubbed “tiger stripes”.

Recently the tiger stripe region has also been found to be emanating a surprising amount of heat, even further supporting a liquid water interior – as well as an internal source of energy. And where there’s liquid water, heat energy and organic chemicals – all of which seem to exist on Enceladus – there’s also a case for the existence of life.

“This finding is a crucial new piece of evidence showing that environmental conditions favorable to the emergence of life can be sustained on icy bodies orbiting gas giant planets.”

– Nicolas Altobelli, ESA project scientist for Cassini

Enceladus has intrigued scientists for many years, and every time Cassini takes a closer look some new bit of information is revealed… we can only imagine what other secrets this little world may hold. Thankfully Cassini is going strong and more than happy to keep on investigating!

“Without an orbiter like Cassini to fly close to Saturn and its moons — to taste salt and feel the bombardment of ice grains — scientists would never have known how interesting these outer solar system worlds are.”

– Linda Spilker, Cassini project scientist at JPL

The findings were published in this week’s issue of the journal Nature.

Jason Major is a graphic designer, photo enthusiast and space blogger. Visit his website Lights in the Dark and follow him on Twitter @JPMajor or on Facebook for the most up-to-date astronomy awesomeness!

Related

Question:
Why don’t we already have a sample and return mission planned to Enceladus to fly a small probe through the plumes of material? It would have to be about the simplest possible scenario we will ever be presented with to search something that has a real chance of having some form of life present. Far simpler than having to land somewhere and get back into orbit again after having to scrape dirt or melt ice etc. If there is any biology there at all, there will be some ‘microbiology’. That being the case some of it is bound to be atomised into space as the sea containing it boils off around it. And we all know how good freeze drying is at preserving microbiological samples…

Ivan’s right, This dumbass of a country called the US cares more about politics than they do about space travel. NASA asking the gov’t for money to build a probe capable of orbiting Enceladus and sampling its plumes would be promptly ignored.

There are good reasons why we don’t have such a mission, and not all of them are political. Saturn is an immense distance away – it’s easy enough to fling a probe past it (which we’ve done many times), but having a probe collect a sample and return means it has to do two things:

Firstly, it has to effectively stop to collect a sample. This would require a lot of fuel to decelerate, and carrying that fuel there will, in turn, require more fuel to get the probe there in the first place. The alternative to all this fuel is to get there at a much slower pace – but equipment tends to degrade in space and the less time spent the more reliable the mission will be.

Secondly, it has to come back. This means it has to generate enough thrust to leave Saturn, which is perhaps even more thrust than it took to leave Earth (and we’ve all seen how much thrust it takes to get a probe off Earth). The probe would effectively have to take its own ridiculously big rocket just to get back to Earth. And that, in turn, would require even more fuel to get it there in the first place.

Now, I admit I haven’t done the necessary calculations. But given my amateur reasoning I am pretty confident that a sample return mission to Saturn, or even Jupiter, is damn-near impossible with our current technology. The amount of fuel required to pull it off would be staggering.

At least the plume fly through was the core of Wayne’s proposal; and a good point.

Btw, if it is a one-time fly-through, could it be combined with a Saturn gravity assist for a return trajectory? I don’t do space “ballistics” much.

While we are at it, no sample return have used fuel for deceleration, besides the Apollos for good reason. They have all used or plan to use ballistic reentry: Luna 16, 20, 24; Stardust; Hayabusa; Hayabusa 2 (planned); Osiris-REx (planned).

Not to support politics unrelated to science here, or even a rational analysis: it is a false choice you present us with as one can do both.

But as for the choice of conflict it is a poor one. Better would have been Afghanistan or Iraq, where no internal part was calling for external help.

In Libya that happened, and the world reacted on moral grounds. Whether that was a correct decision or not (I believe the jury is still out), it was _perceived_ as more important at the time and on good grounds.

For this to be a possibility, there needs to be a mechanism by which the ice particles coalesce into large enough objects… currently we don’t observe this in any of Saturn’s rings due to the “sheperding” effect of the moons (UT has a good article on this somewhere).

There also needs to be a mechanism by which such an object, once formed, is belted out of Saturn’s gravity well without simulatenously being shattered to pieces. I can’t see how this might be achieved.

I know this for a fact. In order for an object that is orbiting Saturn to leave Saturn, a force must be applied to the object and give it the required kinetic energy to escape Saturn’s gravity well.

To give such an object a big enough kick, it would have to be struck by another object (an asteroid for example) with a very large force. However, this would likely shatter the object, especially if it was made of ice.

I cannot think of any other mechanism by which an object could leave Saturn’s gravity well – the required energy has to come from somewhere. Do you have a particular mechanism in mind?

You seem to be invoking possibilities without explaining how those possibilities might exist.

In what possible circumstances could a lump of ice be struck by an object, receive millions of joules of kinetic energy, and not be totally obliterated by the impact? If you’re going to propose a hypothetical, you need to back it up with some figures.

Also, what “internal forces” in the E-ring are you referring to? How big are those forces? What do those forces act on? How would they eject an object? Again, you need to back up your hypothetical.

That, and they probably wouldn’t ever be large enough to penetrate the Earth’s atmosphere without completely burning up. You’d need a pretty big lump (and preferably made of rock) to deliver a microbe in-tact to the surface of the Earth.

This is also assuming that Enceladus has existed (and has been pumping out plumes like this) for 4 billion years.

Edit: it’s an interesting possibility nonetheless, but I think something that would better make good sci-fi than science.

Water water everywhere – it seems like no matter where we look in our solar system (i.e. Mars, Mercury, Earth’s Moon, Enceladus), we find much more water than we ever expected. I think that this significantly raises the chances that we will find life elsewhere and that many of our earlier assumptions (i.e. that the Moon is dry) need to be properly tested in order for us to truly understand planets & life.

I can’t wait til they discover the fishy-type creatures swimming around on Enceladus. Maybe if Cassini got close enough, it could see one of the fishy-type creatures floating around in the E ring. Cassini is the BEST!

I hate to spew salty ice water plumes on the party, but the earliest observation of the material of the plumes still stands as far as I know. The organics are pristine cometary type, which means no biosphere is living of it.

If life was extant or lately extinct we would see modification: subtractions, additions, discontinuous distributions. If anything, Enceladus lack some of the complex organics of some comets, perhaps simply because of salty liquid water breaking bonds.

This has been known for several years.

That doesn’t mean that we shouldn’t check habitability and chemistry. It just means that the likelihood for life is lower than on, say, Titan or in, say, Europa.